Interlamellar boundaries govern cracking
Interlamellar boundaries govern cracking
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DOI：
10.1016/j.actamat.2021.117091
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发表时间：
2021-08
期刊：
影响因子：
9.4
通讯作者：
Shitan Yan;Z. Qi;Yang Chen;Yuede Cao;Jinpeng Zhang;G. Zheng;Fengrui Chen;Ting Bian;
中科院分区：
文献类型：
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作者：
Shitan Yan;Z. Qi;Yang Chen;Yuede Cao;Jinpeng Zhang;G. Zheng;Fengrui Chen;Ting Bian;
与以往对层状材料断裂行为的研究不同，在多合成孪晶（PST）TiAl单晶中发现了一种新现象，即具有裂纹分隔器（Ⅱ型）的试样比具有裂纹止裂器（Ⅰ型）的试样具有更高的韧性。结合微观表征和理论计算，我们揭示了这种相反的现象是由层间边界的相干性引起的。对于具有共格层间边界的PST TiAl单晶，共格层间边界抑制了I型试样的分层，裂纹倾向于沿沿着形变孪晶面穿透层间。而Ⅱ型试样中产生的固着位错阻碍了其它位错的进一步运动，导致裂纹尖端钝化。结果表明，Ⅱ型试样的断裂韧性高于Ⅰ型试样。韧性比，RT=Ttype I/ Ttype II，提出了评估层状材料中不同水平的边界相干性的开裂行为。在以往的研究中，RT> 1是因为它们的边界不连贯，这促进了分层和裂纹尖端钝化。本文的工作揭示了层间边界与裂纹扩展的关系，为层状材料的发展提供了一个新的视角。
Contrary to previous researches of cracking behaviors in lamellar materials, a novel phenomenon has been found in polysynthetic twinned (PST) TiAl single crystals that the specimens with crack divider (type II) own much higher toughness than those with crack arrester (type I). By combining microscopic characterization and theoretical calculation, we reveal that this contrary is caused by the coherency of interlamellar boundaries. For PST TiAl single crystal with coherent interlamellar boundaries, delamination in type I specimen is suppressed by the coherent boundaries and the crack tends to penetrate lamellae along the deformation twinning planes. While sessile dislocations produced in type II specimen hinder the further motion of other dislocations and induce the passivation at crack tip. As a result, the specimen with type II owns higher fracture toughness than that with type I. A toughness ratio, RT=Ttype I/ Ttype II, is proposed to evaluate the cracking behavior with different levels of boundary coherency in lamellar materials. In previous studies, RT> 1 because their boundaries are not coherent, which promotes the delamination and crack tip passivation. The present work sheds light on the relationship of interlamellar boundaries and crack propagation, which provides a new perspective for the development of lamellar materials.